Re: [RFC v2 12/14] xfs: make the calculation generic in xfs_sb_validate_fsb_count()

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Feb 13, 2024 at 10:37:11AM +0100, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> Instead of assuming that PAGE_SHIFT is always higher than the blocklog,
> make the calculation generic so that page cache count can be calculated
> correctly for LBS.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/xfs/xfs_mount.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index aabb25dc3efa..bfbaaecaf668 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -133,9 +133,13 @@ xfs_sb_validate_fsb_count(
>  {
>  	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
>  	ASSERT(sbp->sb_blocklog >= BBSHIFT);
> +	unsigned long mapping_count;

Nit: indenting

	unsigned long		mapping_count;

> +	uint64_t bytes = nblocks << sbp->sb_blocklog;

What happens if someone feeds us a garbage fs with sb_blocklog > 64?
Or did we check that previously, so an overflow isn't possible?

> +
> +	mapping_count = bytes >> PAGE_SHIFT;

Does this result in truncation when unsigned long is 32 bits?

--D

>  
>  	/* Limited by ULONG_MAX of page cache index */
> -	if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
> +	if (mapping_count > ULONG_MAX)
>  		return -EFBIG;
>  	return 0;
>  }
> -- 
> 2.43.0
> 
>